How can I know if my child is depressed

Exhibited symptoms of depression and children, adolescents and adults can look the same; Loss of interest in activities, difficult sleeping, mood swings etc. But particularly, depression in children can be hard to pinpoint as they themselves often can not reflect on or contemplate their own experience. Somatic complaints ('my head hurts' or 'my tummy hurts') irritability, negativity, social withdrawal, and prolonged separation anxiety can be indications of childhood depression.

Yes! Also, check out the article on Childhood Depression.